Re: Kernel patch cases qemu live migration failed.

[Andrew Jones]

On Thu, Oct 15, 2020 at 12:26:10PM +0100, Marc Zyngier wrote:
> Hi
> 
> Please don't use my arm.com address anymore, nobody reads it...
> 
> On 2020-10-15 05:06, 张东旭 wrote:
> > I'm so sorry for disturbing you.
> > 
> > When I apply this kernel patch：KVM: arm64/sve: System register
> > context switch and access support
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm64/kvm/sys_regs.c?id=73433762fcaeb9d59e84d299021c6b15466c96dd
> 
> This patch was only introduced in 5.2, and wasn't supposed to be
> backported to anything else.

All upstream patches are backport candidates. Welcome to RHEL :-)

> 
> > qemu live migration will failed with messages：
> >               ​qemu-kvm: Invalid value 233 expecting positive value
> > <= 232
> >               qemu-kvm: Failed to load cpu:cpreg_vmstate_array_len
> > New version kernel  exclude ID_AA64ZFR0_EL1 register when host not
> > support SVE feature,
> > so qemu ioctl kvm(KVM_GET_REG_LIST) will not contain ID_AA64ZFR0_EL1
> > register.
> > 
> > I'm using CentOS Linux kernel, old kernel version：4.18.0-80.11.el8
> > (migration source)
> >       new kernel version：4.18.0-147.5.el8 (migration destination)
> > 
> > CentOS linux kernel version 4.18.0-111.el8 applied this patch. So
> > 4.18.0-147.5.el8 also applied this patch.
> > 
> > Migration source and destination hosts have the same hardware, just
> > kernel version is different,
> > and the hardware on either side of the migration not support SVE.
> > 
> > Is there some good suggestions，which can make sure old version
> > kernel live migration to new version kernel with qemu?
> 
> I['m afraid you should take this with your distribution of
> choice, unless you can reproduce the problem with mainline kernels.

I'll bet this reproduces when migrating from a mainline pre SVE register
filtering kernel to a mainline that does the filtering. I don't have
time to test that though.

Thanks,
drew